The overall concern of this project is to elucidate the mechanisms that control the morhological development of the early embryonic heart. We are largely confining our efforts to early development (pre septation) stages. We are examining the role of various components of the developing heart in regulating shape. Injection of microliter quantities of biochemically specific enzymes into the cardiac jelly alter the shape of the developing heart in situ. Different enzymes have dramatically different effects. Mechanical factors also seem to regulate early morphogenesis. We have manipulated experimentally a large number of cultured chick embryos (N greater than 100) and are able to reproducibly disturb normal cardiac rotation. Our interventions are entirely physical and involve pericardial regions. This suggests that extra-cardiac influences are important in regulating early heart rotation. We shall continue these studies and, in particular, attempt to discern long term effects of mechanically induced abnormalities. For this purpose we shall attempt to culture chick embryos in vitro for longer periods of time. We are also examining rates of differentiation in myocardial cells derived from right and left precardiac splanchnic mesoderm. We are surgically inducing cardia bifida and harvesting the resulting hearts at staged intervals. For each stage we are measuring intracellular myosin content by means of quantitative immunofluorescence on isolated cells. Additionally, size measurements are being made on freshly isolated cells derived from right and left hearts. These experiments will test directly the hypothesis that intrinsic differences in cells derived from right and left rudiments are responsible for morphogenetic changes.